FeignRequestInterceptor 原理详解

`FeignRequestInterceptor`是 OpenFeign 的请求拦截器机制，其工作原理如下：

1. 核心设计模式

责任链模式：Feign 通过拦截器链在请求发送前和接收后执行自定义逻辑。

// 拦截器接口定义 public interface RequestInterceptor { void apply(RequestTemplate template); }

2. 请求处理流程

Controller ↓ Feign Client ↓ RequestInterceptor.apply() ← 在这里修改请求 ↓ Encoder.encode() ← 序列化请求体 ↓ Client.execute() ← 发送HTTP请求 ↓ Decoder.decode() ← 反序列化响应 ↓ ResponseInterceptor ← 响应拦截器（如果存在） ↓ 返回结果

3. 拦截器工作原理

3.1 注册机制

@Configuration public class FeignConfig { // Spring会自动发现并注册所有RequestInterceptor Bean @Bean public RequestInterceptor myInterceptor() { return template -> { // 拦截逻辑 }; } }

3.2 拦截时机

// Feign内部的执行流程 public class SynchronousMethodHandler { public Object invoke(Object[] argv) { // 1. 构建请求模板 RequestTemplate template = buildTemplateFromArgs.create(argv); // 2. 应用所有拦截器 for (RequestInterceptor interceptor : requestInterceptors) { interceptor.apply(template); } // 3. 发送请求 return client.execute(template, options); } }

4. RequestTemplate 结构

public class RequestTemplate { private String method; // HTTP方法 private String url; // 请求URL private Map<String, String> headers; // 请求头 private byte[] body; // 请求体 private Map<String, String> queries; // 查询参数 // 修改header的方法 public header(String name, String... values) {} public query(String name, String... values) {} }

5. 多拦截器执行顺序

@Component @Order(1) public class AuthInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate template) { // 1. 添加认证header template.header("Authorization", "Bearer token"); } } @Component @Order(2) public class LoggingInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate template) { // 2. 添加日志header template.header("X-Request-Id", UUID.randomUUID().toString()); } } // 执行顺序：AuthInterceptor → LoggingInterceptor

6. 实际应用场景

场景1：传递上游请求头

@Component public class PassThroughInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate template) { // 从当前线程获取请求上下文 ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes(); if (attributes != null) { HttpServletRequest request = attributes.getRequest(); // 传递认证信息 String authHeader = request.getHeader("Authorization"); if (authHeader != null) { template.header("Authorization", authHeader); } // 传递追踪ID String traceId = request.getHeader("X-Trace-Id"); if (traceId != null) { template.header("X-Trace-Id", traceId); } } } }

场景2：添加统一header

@Component public class CommonHeaderInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate template) { // 服务标识 template.header("X-Service-Name", "a-service"); // 调用时间戳 template.header("X-Request-Time", Instant.now().toString()); // 版本号 template.header("X-API-Version", "v1.0"); } }

场景3：请求签名

@Component public class SignInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate template) { // 1. 获取请求参数 String method = template.method(); String url = template.url(); String body = new String(template.body()); // 2. 计算签名 String sign = calculateSign(method, url, body); // 3. 添加签名header template.header("X-Signature", sign); } }

7. 与 Spring 上下文集成

7.1 获取 Spring Bean

@Component public class TokenInterceptor implements RequestInterceptor { @Autowired private TokenService tokenService; // 可以注入其他Bean @Override public void apply(RequestTemplate template) { String token = tokenService.getToken(); template.header("Authorization", "Bearer " + token); } }

7.2 条件性拦截

@Component public class ConditionalInterceptor implements RequestInterceptor, ApplicationContextAware { private ApplicationContext context; @Override public void setApplicationContext(ApplicationContext context) { this.context = context; } @Override public void apply(RequestTemplate template) { // 根据环境决定是否添加header Environment env = context.getEnvironment(); String profile = env.getActiveProfiles()[0]; if ("prod".equals(profile)) { template.header("X-Env", "production"); } } }

8. 调试和日志

@Component @Slf4j public class LoggingInterceptor implements RequestInterceptor { @Override public void apply(RequestTemplate template) { // 记录请求信息 log.info("Feign Request: {} {}", template.method(), template.url()); log.info("Headers: {}", template.headers()); // 添加请求ID以便追踪 String requestId = UUID.randomUUID().toString(); template.header("X-Request-ID", requestId); MDC.put("requestId", requestId); // 设置到日志上下文 } }

9. 错误处理和重试

@Component public class RetryInterceptor implements RequestInterceptor { private ThreadLocal<Integer> retryCount = new ThreadLocal<>(); @Override public void apply(RequestTemplate template) { Integer count = retryCount.get(); if (count == null) { count = 0; } // 标记重试次数 template.header("X-Retry-Count", String.valueOf(count)); retryCount.set(count + 1); } }

10. 性能考虑

@Component public class PerformanceInterceptor implements RequestInterceptor { private ThreadLocal<Long> startTime = new ThreadLocal<>(); @Override public void apply(RequestTemplate template) { startTime.set(System.currentTimeMillis()); } // 响应拦截器（Feign 6+ 支持） public void handleResponse(Response response) { Long start = startTime.get(); if (start != null) { long duration = System.currentTimeMillis() - start; log.info("Feign请求耗时: {}ms", duration); } } }